Steam generating unit



Nova; 13', 1962 E. c. MILLER 3,063,431.

STEAM GENERATING UNIT Filed May 31,v 1961 2 Sheets-Sheet 1 FIG. I.

EARLE 6. MILLER INVENTOR.

' ATTORNEY Nbw I13, 139625 E; c:. MILLER STEAM; GENERAHNG'; UNIT 2 Sheets-Sheet; 2

Filed May 31 1963;.

ATTORNEY 3,063,431 STEAM GENERATING UNIT Earle C. Miller, Worcester, Mass, assignor to Riley Stoker Corporation, Worcester, Mass, a corporation of Massachusetts Fiied May 31, 1961, Ser. No. 113,936 8 Cim'ms. (1. 122-473) This invention relates to a steam generating unit and more particularly to apparatus arranged to generate steam and to regulate the temperature of superheated steam which is produced therein.

There have been many methods suggested in the past for maintaining the temperature of the superheated steam in a steam generating unit at a fixed value, irrespective of changes in load on the unit. Among these methods is that of lay-passing portions of the gas away from sections of superheater heat exchange surface. Also, there is the method in which the temperature of the gases passing over convective superheaters is regulated by regulating the residence time of the gases in the main combustion chamber by the use of tilting burners. There is the method of superheat control by gas recirculation in which gases from the back passes are returned in regulated amounts to the main combustion chamber to increase or decrease the mass How of gases over convection superheater units. Of course, there is also the old method of desuperheaing the superheated steam by injecting a spray of water into it. Another method of controlling superheat is described in the patent to Miller No. 2,947,289, in which the fiame rising vertically through the furnace is moved to various positions between the front wall and the rear wall in order to regulate superheat. There are some boiler conditions under which this last method of controlling superheat does not give a sufficient range of superheat temperature change. While it is true that this method can be combined with desupereating methods and with by-pass methods of superheat control to give sufficient range, these last two methods affect the overall efiiciency of the boiler by discarding heat. These deficiencies in the prior art have been obviated by the present invention in a novel manner.

It is, therefore, an outstanding object of the present invention to provide a steam generating unit having apparatus for the control of superheat in which the heat discarded from the cycle at certain loads is reduced to a minimum value.

Another object of the invention is the provision of an apparatus for the control of superheat whose action is not detrimental to the overall operation of the steam generating unit.

Another object of the invention is the provision of an apparatus for the control of superheat which makes use of the flame-positioning method and in which the range of control has been greatly increased.

A still further object of the present invention is the provision of an apparatus for the control of superheat in which the advantages of the gas recirculation method of superheat control are obtained without the necessity for expensive ducting and controls.

With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.

The character of the invention, however, may be best understood by reference to one of its structural forms, as illustrated by the accompanying drawings in which:

FIG. 1 is a vertical sectional view of a steam generating unit embodying the principles of the present invention;

FIG. 2 is a horizontal sectional view of the unit taken on the line IIII of FIG. 1;

ice

FIG. 3 is a schematic view of the unit to show its operation at low load, and

FIG. 4 is a similar schematic view of the unit taken during high load operation.

In the specification which follows, the expressions longitudinal, transverse refer to those directions as applied to a steam generating unit in the ordinary practice in that art and in general refer to the flow of gas through the unit.

Referring to FIG. 1 first, wherein are best shown the general features of the invention, the steam generating unit, indicated generally by the reference numeral 11, is shown as consisting of a furnace 12 and a boiler 13 mounted on a supporting structure 14. The furnace 2 consists of a forward wall 15 and a rearward wall 16 which, with side walls 17, define a vertically-elongated combustion chamber 18. Underlying the combustion chamber is a slag basin 19 formed of refractory material. The forward wall 15 is provided with a nose 21 located in its lower portion directly overlying the slag basin 19 and provided on its downwardly-directed surface with a burner 22. A similar nose 23 is provided in the rearward wall 16 and a burner 24 is mounted on the downwardly-directed surface of that nose.

The boiler 13 consists of an upper steam-and-water rum 25 joined by downcomer tubes 26 to a lower drum 27, both drums extending transversely of the unit. Large downcomer pipes 28 extend from the lower drum 27 to a header 29 extending around the periphery of the slag basin 19. Water-wall tubes 31 extend upwardly from the header 29 along the forward wall 15, the rearward wall 16, and the side walls 17. These water-wall tubes are connected at .the upper part of the furnace to the steam-and-water drum 25. Every other water-wall tube on the back wall 16 is formed with a forward loop 32. as will be described more fully hereinafter. These tubes serve to define an upper pass 34 between its forwardly projecting portions and the roof 35 of the furnace. A refractory wall 36 extends downwardly from the steam-and-water drum 25 and serves to divide the rearward portion of the unit into back passes 37 and 38. A duct 39 leads from the back pass 38 to a dust collector 41 which, in turn, is connected through a rotary regenerative air heater to an induced draft fan, a breaching and a stack, all not shown but usual in the art.

A force draft fan (not shown) is connected through the air heater to a duct 46 having branch ducts 47 and 48 leading to the burners 24 and 22, respectively. A duct 49 leads from the duct 46 to an attrition-type pulverizer (not shown). Pipes 53 lead from the output of the pulverizer to the burners 22 and 24.

As is evident in FIG. 1, the steam-and-water drum 25 is provided with a separator of the usual type and tubes 54 lead from the upper part of the steam-and-water drum to a header 55 arranged beside the forward wall 15 of the furnace. Below the header 55 is arranged another header 56 of a similar type. Joiningthese headers and lying within the furnace against the forward wall 15 are radiant superheater tubes 57. Tubes 58 lead from the header 56 to a header 59 which is connected through a convection superheater 61 lying in the pass 37 to a convection superheater 62 lying in the upper pass 34. The output of the superheater 62 is connected to superheater platens 63 hanging downwardly from the roof 35 into a restricted passage 33 between the forward wall 15 and the foremost portion of the tube loops 32. The output of the platen 63 is connected to a superheated steam header 64 which, in turn, is connected by a high pressure pipe 65 to the turbine (not shown).

The output of the high pressure section of the turbine (not: shown) is connected by means of a pipe 66 to a header 67 arranged adjacent the rearward wall 16 of the furnace. A similar header 68 is mounted above the header 67 and the two are joined by a radiant reheater 69 which lies closely'adjacent the inner surface of the rearward wall 16. The header 68 is connected by a pipe 71 to an input header 72 connected to one end of a convection reheater 73 lying in the upper pass 34'between the superheater 62 and the superheater platen 63. The output of the reheater 73 is connected to a reheater steam header 74 which, in turn, is connected by means of a high pressure pipe 75 to a low pressure section of the turbine (not shown). The burners 22 and 24 are similar to those described in Patent No. 2,947,289. For instance, in the case of the burner 22 the air duct 48 is connected to a housing 76. Centrally of the housing is located a continuous spark igniter (not shown) and a gun 78 for introducing pulverized coal into the burner. The conduit 53 leading from the pulverizer 51 is connected to the gun and in the central part of the gun is a gas gun to insure ignition. The water-wall tubes 31 are bent rearwardly in the vicinity of the burner 22, to form passages for the flow of fuel and air. At the mouth of theburner below the gun 78 are located pivoted vanes 83 which are connected through a mechanical linkage to an actuating rod 84. In the upper part of the burner are located pivoted vanes 85 which are connected through a mechanical linkage to an actuating rod 86. The burner 24 is similarly provided with a fuel gun 87, lower vanes 88 whose angularity is adjustable by means of an actuating rod 89, and upper pivoted vanes 91 whose angularity is adjustable by means of an actuating rod 69, and upper pivoted vanes 91 whose angularity is adjustable by means of an actuating rod 92.

W The actuating rod 86 for the vanes 85 is connected to the piston rod of a hydraulic linear actuator 96, while the actuating rod d2 of the vanes 91 is connected to a similar actuator 97. The actuator 96 is connected by conduits 98 and 99 to a controller 101 and the linear actuator .97 is connected to the controller by means of V conduits 102 and 103. The. air duct 48 leading to the burner '22 is provided with a control damper 104 which is connected for pivotal action through a mechanical linkage to the piston rod of a linear actuator 105 whose piston is movable under the control of conduits 186 and 197 by which it is connected to the controller 1&1. In a similar manner the duct 47 leading .to the burner 24 is provided with a pivoted damper Hi8 which is connected-through a linkage mechanism to the piston rod of a linear actuator 109. This actuator is connected to the controller 101 by means of conduits 111 and 112. The superheated steam header 64 has mounted therein a temperature-indicating device 113 of the usual type, and this device is connected through a line .114 to the controller 1111 A similar temperature-measuring device 115 resides in the reheated steam header 74 and is connected by a line 116 to the controller 101. The controller 1511 is of the usual type used in temperature control applications; it consists of an apparatus which is well known in the art for converting electrical signals in the lines 114 and 116 into hydraulic flow throughthe'lines 106,107, 98, 99, 111, 112, 102, and 103 leading to the various hydraulic linear actuators associated with the apparatus; since the controller is not partofthe'present invention in its detailed form, it is not felt'that a specific description thereof is not necessary adequately to describe the present invention.

1 -As has been stated, each of the alternate tubes in the rear water-wall tubes of the wall 16 of the furnace have been bent forwardly to form a loop 32 which resides above the combustion chamber. Each tube is bent at an angle of approximately 45 to the vertical to provide a' portion 117 extending forwardly from a position'w ell above the lower drum 27 of the boiler. Each tube is then bent vertically at a position somewhat forwardly of'the midpoint between the front and rear wall of the furnace to provide a vertical portion 118. Each tube is then bent to follow the bottom surface of the roof 35 to provide a roof portion 119. Mounted on the tubes 32 are refractory blocks 121 forming a bafiie 122. This baflie extends partly along the forward parts of the inclined portions 117 of the loops 32 and partly along the lower parts of the vertical portions 113. The rearward edge of the battle is located somewhat forwardly of the rear wall 16 to provide a passage 123 therebetween. The forward edge of the battle is in general alignment with the vertical portion 118 of the tubes 32 and between the'forwa'rd edge of the baffle and the front wall is located the passage 33 leading to the upper pass 34. The convection 'superheater 62 is located entirely above the bafiie 122 and has no substantial portions which are rearwardly' of the rear edge of the baliie. At the same time, the convection reheater 73 is located above the baffle at the forward portion of it and none of the reheater extends forwardly of the forward edge of the baffle or forwardly of the screen provided by the vertical portions 113 of the tubes 32. The superheater platens 63 lie entirely within the passage 33 forwardly of the forward edge of the bafiie and of the vertical portions 118. The refractory blocks 121 fit tightly around the tubes and are bonded together by cement in the usual manner to provide a gas-tight baffle construction.

The operation of the apparatus will now be readily understood in View of the above description. The furnace 12 and theboiler '13 operate in the usual manner. Because of the restricted nature of the bottom of the combustion chamber 18 below the level of the noses 21 and 23, it is very hot and quite complete combustion takes place in this lower high-temperature cell. The gases passing upwardly in the restricted zone between the noses 21 and 23 form a flame which may be manipulated so as to flow close to the front wall 15, close to the rear wall 16, or any position intermediate of the walls. In the sense of flame, the applicant means the line of greatest mass'flow and highest gas temperature which is usually indicated in a furnace as a flame; this flame may or may not be luminous, depending upon various factors such as the nature of the fuel and the completeness of combustion. The flame may be manipulated in a manner described in the above-identified patent of Miller by adjusting the angles of the vanes in the burners through the linear actuators $6 and 97 or by adjusting the air flow through the burners by means of the actuators and 109 which manipulate the dampers 104 and 108.

Referring now to FIGS. 3 and 4, it is evident that the position of the flame 124 is manipulated by changing the angularity of the vanes in the burners. In FIG. 3, which shows the relationships at low load, the flame is shown as rising close to the front wall 15. The fiame 124passe's directly along the front wall 15 and'through the passage 33 between the front edge of the baflie 122 and the front wall. From there, the gas flow is directed under the roof 35 through the upper pass 34. In the process of doing this, these gases pass over the'superheater platens 63, the convection reheater 73, and the convection superheater 62, and eventually pass through the gas olftake leading from the furnace into the backpasses. Because the flame extends upwardly along the front part of the furnace, a zone of reduced pressure is created under the baflle 122 and a flow of gases takes place from the upper pass 34 downwardly through the pass 123 between the back Wall 16 and the rearward edge of the'bafiie 122. Now, it is well known that uncorrected superheat tends to be low atlow loads because of the. rising. character of a convection superheat curve. In the present case, the flame 124 andthe greatest mass of gases passes by the most direct path from the burners to tion to the walls of the furnace to cool the gases. This gives a tendency to a higher superheat temperature. Furthermore, the flame is closer to radiant superheater sections 57 and the superheater platens 63 which absorb considerable heat by radiation from the combustion chamber. Most importantly, however, the gases which flow from the upper pass 34- downwardly through the pass 123 to mix with the gases from the burners to pass upwardly once more through the forward pass 33 constitute a form of gas recirculation which increases the mass flow of gases over the convection superheater surfaces, thus raising the temperature of steam in the superheaters. This recirculation of gases takes place auto matically without the use of ducting, dampers, or complicated controls.

Referring to FIG. 4, which shows the relationships which exist at high load, the flame 124 is shown as being positioned close to the rear wall 16, so that a large percentage of the gases have a tendency to go directly through the rear pass 123 and through the gas oiftake 125 to the backpass 37. Some of the gases, of course, will go upwardly through the forward pass 33, across the upper pass 34, and then through the gas offtake 125, but generally speaking, the greatest volume of gases will go through the pass 123. This has a tendency to lower the temperature of superheat. First of all, there is no recirculation downwardly through the pass 123 as was provided at low load. Secondly, those gases which pass over the convection superheaters 62 and 63 have reached these areas by a longer path since they are forced to first go toward the rear wall of the furnace and then move forwardly to the furnace so that their residence time in the furnace is longer (and their temperature when they reach the convection superheater is lower). Furthermore, the flow of gases over the convection units is smaller in amount; that is to say, the mass flow over the convection superheaters is less. Also, with the flame at the rear of the furnace, the radiation to the radiant superheater 57 and the radiant parts of the superheater platen 63 is less. All of these factors have a tendency to lower superheat. At intermediate loads, of course, the movement of the flame to positions between the front and rear walls will produce variations of these factors and will permit close adjustment of superheat temperature.

It is obvious that minor changes may be made oin the form and construction of the invention without departing from the material spirit thereof. It is not, however, desired to confine the invention to the exact form herein shown and described, but it is desired to include all such as properly come within the scope claimed.

The invention having been thus described, what is claimed as new and desired to secure by Letters Patent, is:

1. A steam generating unit, comprising a combustion chamber having front, rear, and side walls, fuel-burning apparatus located at the bottom of the combustion chamher to produce a mass flow of hot products of combustion, a gas off-take opening into the upper part of the rear wall, a baflle extending across the combustion chamber in a position spaced away from the front wall to provide a passage located between the front wall and the baflie and extending over the baffle, said baflle in cluding means providing an opening located in the baflle immediately adjacent the rear Wall, a convection superheater located in the passage, and positioning means associated with the fuel-burning apparatus to locate the line of greatest mass flow at a desired position between the front wall and the rear wall, the positioning means causing the line of greatest mass flow to be located adjacent the front wall at low load to cause a recirculation of gas from the passage to the underside of the baffle through the said opening and adjacent the rear wall at high load to cause a flow of gas directly through the said opening to the said passage to aid in maintaining the temperature of superheated steam at a predetermined value.

2. A steam generating unit, comprising a verticallyelongated combustion chamber having walls, fuel-burning apparatus located at the bottom of the combustion chamber to produce a flame, a gas off-take opening into the upper part of one of the walls, a baflle extending across the combustion chamber in a position spaced away from the 'wall opposite the said one of the walls to provide a passage located between the Wall opposite the said one of the Walls and the baffle and extending over the battle, said bafl'le including means providing an opening located in the baflle immediately adjacent the said one of the walls, a convection superheater located in the passage, and a flame-positioning means associated with the fuelburning apparatus causing the flame to be located at a position from adjacent the said one of the walls at high load to cause a flow of gas directly through the said opening to the said passage to adjacent the said wall opposite at low load to cause a recirculation of gas from the passage to the underside of the baflle through the said opening to aid in maintaining the temperature of superheated steam at a predetermined value.

3. A steam generating unit, comprising a verticallyelongated combustion chamber having front, rear, and side walls, fuel-burning apparatus located at the bottom of the combustion chamber to produce a flame, a gas offtake opening into the upper part of the rear wall, a baflle extending across the combustion chamber in a position spaced away from the front wall to provide a passage located between the front wall and the battle and located over the baffle, said batfle including means providing an opening located in the baffle immediately adjacent the rear wall, a convection superheater located in the passage, and means associated with the fuel-burning apparatus to position the flame at a desired position between the front wall and the rear wall, the flame-positioning means causing the flame to be positioned adjacent the front wall at low load to cause a recirculation of gas from the passage to the underside of the baffle through the said opening and adjacent the rear wall at high load to cause a flow of gas directly through the said opening to the said passage to aid in maintaining the temperature of superheated steam at a predetermined value.

4. A steam generating unit, comprising a verticallyelongated combustion chamber having front, rear, and side walls covered with water-wall tubes, fuel-burning apparatus located at the bottom of the combustion chamber to produce a flame, a gas off-take opening into the upper part of the rear wall, alternate tubes of the rear wall extending forwardly from a position adjacent the gas off-take and then extending upwardly, a baffle mount ed on the saidalternate tubes and extending across the combustion chamber in a position spaced away from the front wall to provide a passage located between the front wall and the baffle and extending over the baffle, said baffle including means providing an opening located in the baflle immediately adjacent the rear wall, a convection superheater located in the passage, and means associated with the fuel-burning apparatus to position the flame at a desired location between the front wall and the rear wall, the flame-positioning means causing the flame to be positioned adjacent the front wall at low load to cause a recirculation of gas from the passage to the underside of the baffle through the said opening and adjacent the rear wall at high load to cause a flow of gas directly through the said opening to the said passage to aid in maintaining the temperature of super-heated steam at a predetermined value.

5.A steam generating unit, comprising a verticallyelongated combustion chamber having front, rear, and side walls and a roof, fuel-burning apparatus locatedat the bottom of the combustion chamber to produce a flame, a gas off-take opening into the upper part of the rear wall, a baflle extending across the combustion chamber in a position spaced away from the front wall to provide a passage located between the front wall and the baflie and extending between the baflle and the roof, said baffle including means providing an opening located in the bafiie immediately adjacent the rear wall, a convection superheater located in the passage, superheater platens hanging downwardly between the bafile and the front wall into 'thecombustion chamber, and means associated with the fuel-burning apparatus to position the flame at a desired position between the front wall and the rear wall, the flame-positioning means causing the flame to be positioned adjacent the front wall at low load to cause a recirculation of gas from the passage to the underside ofthe bafile through the said opening and adjacent the rear Wall at high load to cause a flow of gas directly through the said opening to the said passage to aid in maintaining the temperature of superheated steam at a predetermined value.

6. A steam generating unit, comprising a verticallyelongated combustion chamber having front, rear, side, and roof walls covered with water-wall tubes, fuel-burning apparatus located at the bottom of the combustion chamber to produce a flame, a gas off-take opening into the upper part of the rear wall, alternate tubes of the rear wall extending forwardly from a position adjacent the gas take-oil and then extending upwardly, a bafile mounted on the said alternate tubes and extending across the combustion chamber in a position spaced away from the front wall to provide a passage located between the front wall and the baffle and extending between the baflie and the roof wall, said baifie including means providing an opening located in the baffle and immediately adjacent the rear wall, a convection superheater located in the passage, superheater platens hanging downwardly between the bafile and the front wall into the combustion chamber, and means associated with the fuel-burning apparatus to position the flame at a desired location between the front wall and the rear wall, the flame-positioning means causing the flame to be located adjacent the front wall at low load to cause a recirculation of gas from the passage to the underside of the battle through the said opening and adjacent the rear wall at high load to cause a flow of gas directly through the said opening to the said passage to aid in maintaining the temperature of superheated steam at a predetermined value.

7. A steam generating unit, comprising a verticallyelongated combustion chamber having front, rear, side, and roof walls covered with water-wall tubes, fuel-burn ing apparatus located at the bottom of the combustion chamber to produce a flame, a radiant superheater located adjacent the front wall, a radiant reheater located adjacent the rear wall, a gas off-take opening into the upper part of the rear wall, alternate tubes of the rear wall extending forwardly and upwardly from a position adjacent the gas oif-taketojfor man inclined portion and extending vertically toprovide a vertical portion, a baffie mountedjon the adjoining partsjof the inclined and vertical portions of the said alternate tubes and extending across the combustion chamber to provide a passage located between the front wall and the front edge of the bafile and extending between the upper surface of the baffle and the roof wall, said baffie including means providing an opening located in the baffie immediately adjacent the rear wall, a convection superheater located in the passage, superheater platens hanging downwardly between the baffle and the front wall below the lowermost portion of the baffle into the combustion chamber, and flame-positioning means associated with the fuelburning apparatus to cause the flame to be located in a position from adjacent the front wall at low load to cause a recirculation of gas from the passage to the underside of the baffle through the said opening to adjacent the rear wall at high load to cause a flow of gas directly through the said opening to the said passage to aid in maintaining the temperature of superheated steam at a predetermined Value.

8. A steam generating unit, comprising a verticallyelongated combustion chamber having walls, fuel-burning apparatus located at the bottom of the combustion chamber to produce a flame, a gas off-take opening into the upper part of the furnace, a bafile extending across the combustion chamber in a position spaced away from one of the walls to provide a passage located between the said one of the walls and the bafde, said bafile including means providing an opening located in the baffle immediately adjacent a wall opposite the said one of the walls, a convection superheater located in the passage, and flamepositioning means associated with the fuel-burning apparatus causing the flame to be located at a position from adjacent the said one of the walls at low load to cause a recirculation of gas from the passage to the underside of the baflle through the said opening to adjacent the said opposite wall at high load to cause a flow of gas directly through the said opening to "the said passage to aid in maintaining the temperature of superheated steam at a predetermined value.

References flited in the file of this patent UNITED STATES PATENTS Miller Aug. 2, 1960 

